Battery protection circuit

ABSTRACT

A battery protection circuit includes an abnormal condition detection circuit having a resistor through which a current flows from a load in response to a current flowing in the load. The resistor generates a voltage in response to the current flowing in the load. The battery protection circuit further includes a control circuit having a detection stop switch configured to control the current flowing in the resistor from the load. The control circuit turns off the detection stop switch and a protection switch connected between the battery and the load when the abnormal condition detection circuit detects the abnormal condition according to the voltage generated by the resistor. The control circuit returns the detection stop switch to an ON state after returning the protection switch to an ON state in response to a start of supplying power from the battery to the battery protection circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a battery protection circuit,and especially to a battery protection circuit that detects an abnormalcondition of the battery and turns off a switch connected between thebattery and a load.

2. Description of the Related Art

Japanese Patent Application Publication No.6-303728 discloses aprotection circuit that detects current supplied from a battery to aload and disconnects the load from the battery so as to protect thebattery when an overcurrent condition is detected.

FIG. 2 is a block diagram illustrating an example of a conventionalbattery protection system 1.

The conventional battery protection system 1 comprises a battery 11, abattery protection unit 12, and a load 13.

The battery 11 includes a primary battery such as a manganese dioxidebattery, an alkaline battery and the like or a secondary (rechargeable)battery such as a nickel-cadmium battery, a lithium ion battery and thelike. A positive electrode of the battery 11 is connected to a terminalTB+ of the battery protection unit 12. On the other hand, a negativeelectrode of the battery 11 is connected to a terminal TB− of thebattery protection unit 12.

The battery protection unit 12 comprises a battery protection circuit21, a switch 22, a reset switch 23, a resistor R11, and capacitors C11and C12. The battery protection unit 12 detects abnormal conditions suchas an overcurrent condition and a short circuit condition in response toa voltage of a terminal TL−. When the abnormal conditions are detected,the switch 22 is turned off so as to protect the battery 11 from theovercurrent condition or the short circuit condition.

The terminal TB+ is connected to the terminal TL+ through the resetswitch 23. In addition, the terminal TB+ is connected to the terminalTB− through the resistor R11 and the capacitor C11. Moreover, theterminal TB− is connected to the terminal TL− through the switch 22.

The battery protection circuit 21 includes terminals, Tdd, Tss, Tin,Tout and Tct. The terminal Tdd is connected to a junction point betweenthe resistor R11 and the capacitor C11. Accordingly, a voltage decreasedby the resistor R11 and smoothed by the capacitor C11 is applied to thebattery protection circuit 21 as a driving voltage VDD.

The terminal Tss is connected to the terminal TB−. The terminal Tin isconnected to the terminal TL−. The terminal Tout is connected to a gateof a transistor comprising the switch 22. The terminal Tct is connectedto the terminal TB− through the capacitor C12.

The battery protection circuit 21 further includes a resistor R21 fordetection, an overcurrent detection circuit 31, a delay circuit 32, ashort-circuit detection circuit 33, an output circuit 34, a logiccircuit 35, and a switch 36.

As for the resistor R21 for detection, one end thereof is connected tothe terminal Tin through the switch 36. While the switch 36 is turnedon, the resistor R21 generates a voltage in response to a currentflowing from the terminal Tin. The voltage generated by the resistor R21is supplied to the overcurrent detection circuit 31 and theshort-circuit detection circuit 33.

The overcurrent detection circuit 31 comprises a comparator 41 and areference voltage source 42. The voltage generated by the resistor R21is supplied to an inverting input terminal of the comparator 41. On theother hand, the first reference voltage from the reference voltagesource 42 is applied to a non-inverting input terminal of the comparator41.

When the voltage of the resistor R21 is greater than the first referencevoltage from the reference voltage source 42, the comparator 41determines that the circuit is in the overcurrent condition and sets theoutput level to low. On the contrary, when the voltage of the resistorR21 is smaller than the first reference voltage from the referencevoltage source 42, the comparator 41 determines that the circuit is inthe normal condition and sets the output level to high. The output ofthe comparator 41 is supplied to the delay circuit 32.

The delay circuit 32 comprises a constant current source 51, a switch52, a comparator 53, a reference voltage source 54 and a capacitor C21.

The constant current source 51 supplies a constant current to one end ofthe switch 52. The other end of the switch 52 is connected to thecapacitor C21. When the output level of the overcurrent detectioncircuit 31, i.e., the output level of the comparator 41 is set to low,the switch 52 is turned on. On the contrary, when the output level ofthe comparator 41 is set to high, the switch 52 is turned off. One endof the capacitor C21 is connected to both a non-inverting input terminalof the comparator 53 and the terminal Tct. The terminal Tct is connectedto the terminal TB− through the capacitor C12.

When the switch 52 is turned on, the capacitors C12 and C21 are charged.The charging voltage of the capacitors C12 and C21 is applied to thenon-inverting input terminal of the comparator 53. On the other hand, toan inverting input terminal of the comparator 53, the second referencevoltage from the reference voltage source 54 is applied.

As the overcurrent condition continues, the charging voltage of thecapacitors C12 and C21 becomes greater than the second reference voltagefrom the reference voltage source 54. Then, the comparator 53 sets theoutput level to high. The output of the comparator 53 is supplied to theoutput circuit 34.

The short-circuit detection circuit 33 comprises a comparator 61 and areference voltage source 62. The voltage generated by the resistor R21is applied to a non-inverting input terminal of the comparator 61. Onthe other hand, to an inverting input terminal of the comparator 61, thethird reference voltage from the reference voltage source 62 is applied.When a short occurs between the terminals TL+ and TL−, the voltage ofthe terminal Tin becomes greater than the third reference voltage fromthe reference voltage source 62. Then, the comparator 61 sets the outputlevel to high. The output of the comparator 61 is supplied to the outputcircuit 34.

The output circuit 34 comprises a NOR circuit. The NOR circuit outputs aNOR operation result obtained from the output of the delay circuit 32and the output of the short-circuit detection circuit 33. The outputcircuit 34 sets the output level to low when the output level of thedelay circuit 32 becomes high owing to the continuous overcurrentcondition or when the output level of the short-circuit detectioncircuit 33 becomes high owing to the short-circuit between the terminalsTL+ and TL−. To the contrary, the output circuit 34 sets the outputlevel to high when the output level of the delay circuit 32 is low thatindicates non-overcurrent condition and when the output level of theshort-circuit detection circuit 33 is low that indicatesnon-short-circuit condition since the short does not occur between theterminals TL+ and TL−.

The output of the output circuit 34 is supplied to the terminal Tout.The output of the terminal Tout is supplied to a gate of an N-channelMOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) comprisingthe switch 22. The switch 22 is turned on when the output level of theoutput circuit 34 is high in which neither the overcurrent condition northe short-circuit condition are detected. When the switch 22 is turnedon, current is supplied from the battery 11 to the load 13.

Moreover, the switch 22 is turned off when the output level of theoutput circuit 34 is low in which the overcurrent condition or theshort-circuit condition is detected. When the switch 22 is turned off,the terminal TB− is disconnected from the terminal TL− so that thecurrent is prevented from being supplied from the battery 11 to the load13. Accordingly, the battery 11 and the load 13 are protected from theovercurrent and short-circuit conditions.

The logic circuit 35 connected to the terminals Tdd and Tout switchesthe switch 36 in response to the output voltages of the terminals Tddand Tout. The logic circuit 35 turns off the switch 36 when the outputvoltage of the terminal Tout becomes low because of the overcurrentcondition or the short circuit condition. On the other hand, the logiccircuit 35 turns on the switch 36 when a driving voltage VDD applied tothe terminal Tdd becomes greater than a predetermined voltage. Thus, theovercurrent condition and the short-circuit condition can be detectedagain.

According to Japanese Laid-Open Patent Application Publication No.6-303728, in the battery protection system 1, when the switch 22 isturned off for the emergency protection, the reset switch 23 is turnedoff so as to return the switch 22 to the ON state. One end of the resetswitch 23 is connected to a junction point (node) between the terminalTB+ and an end of the resistor R11. The other end of the reset switch 23is connected to the terminal TL+. When the reset switch 23 is turnedoff, the load 13 is disconnected from the battery protection circuit 21.Accordingly, the current does not flow through the terminal Tin; andthus, the overcurrent and short-circuit conditions are eliminated.Therefore, the switch 22 is turned on.

In the conventional battery protection circuit, once the switch 22 isturned off owing to the abnormal condition, unless the battery 11 isonce released and reconnected while the load 13 is disconnected, theswitch 22 remains in the OFF state. Thus, it is impossible to return toa normal driving condition. Accordingly, the reset switch 23 isindispensable. Therefore, there is a problem in which flexibility ofdesign is restricted.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a batteryprotection circuit that substantially obviates one or more problemscaused by the limitations and disadvantages of the related art.

It is another and more specific object of the present invention toprovide a battery protection circuit that can return the circuit from abattery protecting condition to a normal driving condition by onlyreleasing and reconnecting the battery.

To achieve these and other advantages in accordance with the purpose ofthe invention, an embodiment of the invention provides a batteryprotection circuit that includes an abnormal condition detection circuithaving a current detection resistor through which a current flows from aload in response to a current flowing in the load. The resistorgenerates a voltage in response to the current flowing in the load. Theabnormal condition detection circuit is able to detect an abnormalcondition of a battery according to the voltage generated by theresistor. The battery protection circuit further includes a controlcircuit having a detection stop switch configured to control the currentflowing in the resistor from the load. The control circuit is able toturn off the detection stop switch and a protection switch connectedbetween the battery and the load when the abnormal condition detectioncircuit detects the abnormal condition. The control circuit returns thedetection stop switch to an ON state after returning the protectionswitch to an ON state in response to a start of supply of power from thebattery to the battery protection circuit.

According to at least one embodiment of the present invention, thecontrol circuit includes a power-on-reset circuit able to output a resetsignal when the voltage of the battery is applied to the batteryprotection circuit, and a latch circuit able to reset an output thereofin response to the reset signal output from the power-on-reset circuit.The control circuit returns the protection switch to the ON state by theoutput of the latch circuit being reset.

According to at least one embodiment of the present invention, theabnormal condition detection circuit further includes an overcurrentdetection circuit able to compare the voltage generated by the resistorwith the first reference voltage and output an overcurrent signal whenthe voltage generated by the resistor is greater than the firstreference voltage, and a delay circuit including a capacitor. The delaycircuit is able to charge the capacitor when the overcurrent signal issupplied from the overcurrent detection circuit and output an abnormalsignal when a charging voltage of the capacitor is greater than thesecond reference voltage. The abnormal condition detection circuitfurther includes a short-circuit detection circuit able to compare thevoltage generated by the resistor with the third reference voltage andoutput an abnormal signal when the voltage generated by the resistor isgreater than the third reference voltage. The control circuit furtherincludes an output circuit able to turn off the protection switch whenthe abnormal signal is supplied from one of the delay circuit and theshort-circuit detection circuit, and a logic circuit able to turn offthe detection stop switch after the protection switch is turned off byan output of the output circuit.

According to at least one embodiment of the present invention, the logiccircuit monitoring the voltage of the battery returns the detection stopswitch to the ON state in response to a start of supplying the voltageof the battery to the battery protection circuit.

According to at least one embodiment of the present invention, thebattery protection circuit further includes a reset switch configured tocontrol a voltage supplied from the battery to the control circuit.

According to the present invention, the protection switch is returned tothe ON state in response to the start of supplying the voltage from thebattery to the control circuit. Thus, it is possible to return theprotection switch to the ON state by just releasing and reconnecting thebattery. Therefore, flexibility of design can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating an example of a batteryprotection system according to an embodiment of the present invention;and

FIG. 2 is a block diagram illustrating an example of a conventionalbattery protection system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention are describedwith reference to the accompanying drawings.

FIG. 1 is a block diagram illustrating an example of a batteryprotection system according to an embodiment of the present invention.In FIG. 1, the same components as shown in FIG. 2 are given the samereference numerals, in which descriptions thereof are omitted.

A battery protection system 100 according to the present embodimentdiffers from the battery protection system 1 shown in FIG. 2 in theconfiguration of a battery protection circuit 121 comprising a batteryprotection unit 112.

The battery protection circuit 121 according to the present embodimentcomprises, for example, an IC. The battery protection circuit 121 isconfigured so that a power-on-reset circuit 131 and a latch circuit 132are added to the battery protection circuit 21 shown in FIG. 2.

The power-on-reset circuit 131 monitors the driving voltage VDD appliedto the terminal Tdd and outputs a reset signal when the driving voltageVDD becomes greater than the predetermined voltage. The reset signaloutput from the power-on-reset circuit 131 is supplied to the latchcircuit 132.

The latch circuit 132 is connected between an output terminal of thedelay circuit 32 and an input terminal of the output circuit 34.Regardless of the output of the delay circuit 32, an output level of thelatch circuit 132 is reset to low in response to the reset signal outputfrom the power-on-reset circuit 131. The output of the latch circuit 132is supplied to the output circuit 34. At this moment, the switch 36remains in the OFF state. The output level of the short-circuitdetection circuit 33 is set to low.

Since the output level of the short-circuit detection circuit 33 and theoutput level of the latch circuit 132 are set to low, the output levelof the output circuit 34 is set to high. As the output level of theoutput circuit 34 is set to high, the switch 22 is turned on. As theswitch 22 is turned on, it is possible to supply power from the battery11 to the load 13.

After the switch 22 is turned on, the logic circuit 35 turns on theswitch 36 later. This can be performed, for example, if a thresholdvalue of the power-on-reset circuit 131 is set smaller than thethreshold value of the logic circuit 35. Accordingly, it is possible toreturn the switch 22 to the ON state by disconnecting and reconnectingthe driving voltage VDD applied to the terminal Tdd.

According to the present embodiment, the switch 22 can be returned tothe ON state by only switching on and off the reset switch 133 where oneend thereof is connected to the terminal TB+ and the other end thereofis connected to the junction point (node) between the resistor R11 andthe terminal TL+.

MODIFIED EXAMPLE

In the embodiment above, each of the battery protection circuit 121 andthe switch 22 is formed as a different component. However, the batteryprotection circuit 121 and the switch 22 can be mounted on the samesemiconductor chip.

APPLICATION EXAMPLE

The battery protection unit 112 according to the present embodiment isable to detect an overdischarge of the secondary (rechargeable) battery.

Further, the battery protection unit 112 may be mounted on a battery boxso as to be configured as a set. In this case, the battery protectionunit 112 may be formed as a COB module.

It should be noted that the load 13 may be a DC motor, a light bulb, asilicon audio system utilizing a memory, and the like.

Moreover, the present invention can be applied as a substitute for afuse of devices such as a circuit breaker and an ammeter in which anovercurrent is likely to flow.

Further, the present invention is not limited to these embodiments, butvariations and modifications may be made without departing from thescope of the present invention.

The present application is based on Japanese Priority ApplicationNo.2005-160140 filed on May 31, 2005, with the Japanese Patent Office,the entire contents of which are hereby incorporated by reference.

1. A battery protection circuit comprising: an abnormal condition detection circuit including a current detection resistor through which a current flows from a load in response to a current flowing in the load, said resistor generating a voltage in response to the current flowing in the load, said abnormal condition detection circuit being able to detect an abnormal condition of a battery according to the voltage generated by the resistor; and a control circuit including a detection stop switch configured to control the current flowing in the resistor from the load, said control circuit being able to turn off the detection stop switch and a protection switch connected between the battery and the load when the abnormal condition detection circuit detects the abnormal condition; wherein said control circuit returns the detection stop switch to an ON state after returning the protection switch to an ON state in response to a start of supplying power from the battery to the battery protection circuit.
 2. The battery protection circuit as claimed in claim 1, wherein said control circuit includes a power-on-reset circuit able to output a reset signal in response to the start of supplying power from the battery to the battery protection circuit, and a latch circuit able to reset an output thereof in response to the reset signal-output from the power-on-reset circuit, said control circuit returning the protection switch to the ON state by the output of the latch circuit being reset.
 3. The battery protection circuit as claimed in claim 1, wherein the abnormal condition detection circuit further includes: an overcurrent detection circuit able to compare the voltage generated by the resistor with a first reference voltage and output an overcurrent signal when the voltage generated by the resistor is greater than the first reference voltage; a delay circuit including a capacitor, said delay circuit being able to charge the capacitor when the overcurrent signal is supplied from the overcurrent detection circuit and output an abnormal signal when a charging voltage of the capacitor is greater than a second reference voltage; and a short-circuit detection circuit able to compare the voltage generated by the resistor with a third reference voltage and output an abnormal signal when the voltage generated by the resistor is greater than the third reference voltage; and wherein said control circuit further includes: an output circuit able to turn off the protection switch when the abnormal signal is supplied from one of the delay circuit and the short-circuit detection circuit; and a logic circuit able to turn off the detection stop switch after the protection switch is turned off by an output of the output circuit.
 4. The battery protection circuit as claimed in claim 3, wherein the logic circuit monitoring a voltage of the battery returns the detection stop switch to the ON state in response to a start of supplying the voltage of the battery to the battery protection circuit.
 5. The battery protection circuit as claimed in claim 1, further comprising a reset switch configured to control a voltage supplied from the battery to the control circuit. 